This application claims the priority of German Patent Application Serial No. 100 58 475.6 filed on Nov. 24, 2000, the subject matter of which is incorporated herein by reference.
The present invention relates an infinitely variable cone pulley transmission and generating of axial contact pressures exerted by the cone pulleys onto a traction means, rotating between these cone pulleys, via tensioning means arranged on the transmission shafts, which act in axial direction onto respectively one cone pulley that can be axially displaced along the respective transmission shaft. For this, hydraulic means are provided on a first transmission side for adjusting and maintaining the transmission ratio and a spring that is braced against a support, fixed relative to the shaft, is provided on the second transmission side.
A cone pulley transmission of this type is known, among other things, from German reference DE 43 00 879 and is used whenever a cost-effective transmission is desired for small vehicles and simple industrial applications. The disadvantage of the known transmission, however, is its inability to generate load-dependent contact pressure forces between cone pulleys and traction means. Rather, the spring that generates the contact pressure force on one of the transmission sides determines the output limit for the transmission. In other words, it means that the spring must be designed for a certain maximum output that can be transmitted by the transmission. With a low power transmission, the transmission therefore operates with an excess contact pressure between cone pulleys and traction means and thus with a more or less high loss.
In order to generate the above-mentioned contact pressure forces load-dependent and with the lowest possible losses, it is known that these contact pressure forces can be generated with corresponding control and exclusively with hydraulic means on both transmission sides. Another option is to generate the contact pressure forces purely mechanical, with the aid of so-called contact pressure mechanisms.
A third option consists in the combination of these two systems, for example as disclosed by the subject matter of German references 2 016 181 and 2 058 399. According to the aforementioned reference, the contact pressure forces on both transmission sides are generated load-dependent with contact pressure mechanisms of the aforementioned type. These mechanisms are parallel connected to a device for generating hydraulic contact pressure forces for adjusting and maintaining the transmission gearing. With respect to the design, it means that the respective axially displaceable cam sleeve of the contact pressure mechanism is also positioned axially displaceable on a neck-type extension of the cone pulley, which can be displaced in axial direction to vary the transmission ratio, and is stressed in the direction toward the contact pressure mechanism cam sleeve that is fixed relative to the shaft by a compression spring, arranged between displaceable cam sleeve and adjacent cone pulley. This type of design is extremely space consuming, especially in radial direction, and is thus too costly for simple cone pulley transmissions, especially when considering the scope of the hydraulic control required to adjust and maintain the transmission ratio.
It is the object of the invention to develop a more effective cone pulley transmission of the aforementioned type, which has a mechanical device for the load-dependent generating of contact pressure forces, but does not require additional space on the transmission side in question, particularly in radial direction.
This object is solved according to the invention by arranging on the second transmission side one axially fixed cone pulley and one axially movable cone pulley that is provided with an extended hub. The object is further solved by connecting the cone pulleys so as to rotate together and such that they rotate jointly on their transmission shaft and are coupled to this shaft via a contact pressure mechanism depending on the rotational moment or a rotational moment and the transmission ratio. The object is furthermore solved in that the contact pressure mechanism consists of a cam sleeve, fixed relative to the shaft, a cam sleeve formed by the free end of the extended hub, as well as roll bodies, which are inserted between the opposite-arranged cam tracks and rotate around axes that are positioned radial relative to the transmission shaft, so as to transmit the forces. The roll bodies are guided by rings, are held at a mutual distance to each other and arc adjusted in axial direction with spring force to remain in the region of the axial center between the cam sleeves by a spring that is arranged coaxial on the extended hub.
These measures according to the invention make it possible for the transmission side with mechanical generating of the contact pressure forces to generate these contact pressure forces load-dependent and thus only within the scope required for the momentary output transmitted by the transmission. The purpose of the spring that is now connected parallel to the contact pressure mechanism is reduced to providing a basic contact pressure in case the transmission is idling and no contact pressure force is generated by the contact pressure mechanism. The transmission thus can operate without specific losses.
Since the axially displaceable cam sleeve for the contact pressure mechanism is now integrated into the free end of the extended hub of the associated cone pulley, a design results that requires comparatively no additional space in radial direction. In particular, it is not necessary to arrange the axially displaceable cam sleeve of the contact pressure mechanism as additional component radially outside of the extended hub of the axially displaceable cone pulley, as is necessary for the above-described case.
Since the axially displaceable cam sleeve of the contact pressure mechanism is now an integral component of the axially displaceable cone pulley, as mentioned before, it means that this cam sleeve always assumes only an axial position that corresponds to the transmission-ratio dependent axial position of the displaceable cone pulley. In the event that no load is applied to the transmission, it would then be possible for the roll bodies to assume a position at the bottom of the cam curves formed by the cam sleeves. If a load is applied once more, a spinning of the cam sleeves could result, at least in those gearing positions of the transmission where the cone pulleys of the second transmission side are positioned close together. To keep this from happening, the additional feature of the invention ensures that the roll bodies are always kept in the region of the axial center between the cam sleeves, even in the case of a non-loaded transmission, meaning an idling transmission.
In a manner known per se, it has proven advantageous that the of the second transmission side are arranged on a hollow shaft, which is positioned so as to rotate on the transmission shaft but cannot be displaced in axial direction. It is furthermore advantageous that the axially fixed cone pulley is rigidly connected to the hollow shaft, the axially displaceable coney pulley is connected rotatingly to the hollow shaft and the cam sleeve that is fixed relative to the shaft is arranged next to the hollow shaft on the transmission shaft, such that it rotates along and cannot be moved axially, at least not in the direction away from the opposite arranged cam sleeve. The axially fixed cone pulley in this case can form one piece with the hollow shaft.
One embodiment of the invention advantageously provides that the roll bodies, having pinions that project radially from the roll bodies toward the transmission shaft and are coaxial to their rotational axes, engage in corresponding recesses in the rings. For this, a holding ring that is coaxial to the shaft can be arranged radial to the transmission shaft inside or outside of the roll bodies, wherein the pinions of the roll bodies are positioned so as to rotate inside holding ring bores that are positioned radial to the transmission shaft.
According to one design, a guide ring in the form of a hollow-cylindrical sleeve can be arranged radial to the transmission shaft, outside of the roll bodies, which encloses the roll bodies as well as the extended hub. The guide ring can be arranged so as to be displaceable, but non-rotating relative to the hub, in axial direction along the extended hub while outward projecting pinions on the roll bodies are positioned so as to rotate inside circumferential slots that extend along a radial plane of the transmission shaft. The axial width of these slots corresponds to the diameter of the pinions and the pinions are furthermore held in the axial center region between the cam sleeves. The length of the circumferential slots in circumferential direction corresponds at least to half the maximum mutual circumferential path covered by the cam sleeves for the contact pressure mechanism. Furthermore, the guide ring end facing the axially movable cone pulley is connected to the spring in such a way that moving in the same direction, it also traverses essentially half the axial path of the movable cone pulley each time.
For this, the spring can be braced against the axially displaceable cone pulley as well as against the cam sleeve that is fixed relative to the shaft. In further detail, the arrangement can actually be a disk spring assembly, one half of which is essentially arranged on the hub and the other half on the guide ring. The spring can be braced against the cam sleeve via a hollow-cylindrical intermediate segment that encloses the guide ring, wherein the guide ring is caught between the two halves of the disk spring assembly with a radially outward pointing collar at the end.
To ensure that the guide ring and thus also the circumferential slots remain in the position assigned to the cam curves for the cam sleeve, the guide ring section located on the hub is advantageously provided with at least one groove extending parallel to the transmission shaft. A pin supported by the hub engages in this groove to prevent rotation.
The above-described first design also ensures that the roll bodies are always held with spring action in the axial center between the two cam sleeves of the contact pressure mechanism, even if no load is applied to the transmission. On the other hand, they can also move unhindered to the degree necessary in circumferential direction along with the cam curves of the contact pressure mechanism because of the guide ring. This ensures that the roll bodies always engage in the cam curves, even if the transmission is switched from the idle state back to a load condition.
The same result is achieved with a second embodiment of the invention. With this embodiment, a guide ring is arranged radial to the transmission shaft outside of the roll bodies, which takes the form of at least one assembly of axially side-by-side arranged, ring-shaped corrugated springs with reciprocating undulations in axial direction along the circumference. The guide ring furthermore is captured in axial direction between a collar supported by the hub and a rotating collar supported by the cam sleeve, fixed relative to the shaft, and is held in the axial center position relative to the contact pressure mechanism. Radially outward projecting pinions on the roll bodies furthermore are positioned so as to rotate in the axial center region of this guide ring., Thus, a design has been developed, which ensures the axial center positioning of the roll bodies between the cam sleeves of the contact pressure mechanism, independent of the spring that guarantees the basic contact pressure of the axially displaceable cone pulley.
As modification of this solution, the guide ring can be provided, which is composed of two identical, axially side-by-side arranged corrugated spring assemblies, wherein the corrugated springs of each assembly are braced against each other and are fixedly connected to each other via undulation crest that face each other. The pinions on the roll bodies are positioned so as to rotate between the corrugated disk spring assemblies. To achieve the latter, the holding ring is advantageously arranged outside of the roll bodies, between these and the guide ring composed of corrugated springs, and is provided with a rotating collar that projects radially outward from its axial center and extends between the corrugated spring assemblies. For this, the bores in the holding ring for the roll body pinions can also extend through the collar. If, according to another feature of the invention, the axial width of the collar corresponds to the thickness of the roll body pinions, only circumferential sections of the collar remain between the pinions of neighboring roll bodies, as seen in circumferential direction. This represents a particularly space-saving and weight-saving design.
The spring that ensures the basic contact force of the axially displaceable cone pulley for this design can be arranged on the hub and can be braced against the axially movable cone pulley as well as against the cam sleeve that is fixed relative to the shaft via an essentially hollow-cylindrical intermediate segment that extends past the guide ring. Furthermore, the guide ring collar supported by the cam sleeve, which is fixed relative to the shaft, and the intermediate segment can be combined to form one component.
A cone pulley transmission of the type discussed herein requires that for a change in the transmission ratio, which requires emptying the pressure cylinder arranged on the first transmission side, the necessary axial force is derived via the traction means from the contact pressure force exerted upon the traction means on the second transmission side. This force is also sufficient for a rapid adjustment of the transmission ratio if the transmission operates under normal load conditions. However, if the transmission is in the idle state or at a standstill, only the spring ensuring the basic contact pressure is active on the second transmission side. However, the force exerted by this spring, which is further reduced during the movement to the first transmission side as a result of frictional forces, is only sufficient for a relatively slow adjustment of the transmission ratio in the above-mentioned cases. Added to this is the fact that the pressure medium that must be pushed out of the pressure cylinder must also pass by the correspondingly adjusted control valve while overcoming corresponding resistances.
According to a modified version of the invention, a reversing valve is installed in the intake line for the pressure medium to counteract this effect, which reversing valve can connect the pressure chamber to the pressure medium supply or the suction-in side of a pressure medium pump. As a result of this measure, the pressure medium at least can flow unhindered from the pressure cylinder. The cross section for a discharge of this type without problems is dimensioned accordingly large. It is also possible to suction the pressure medium from the pressure cylinder, meaning the adjustment of the transmission ratio is actively encouraged.
It is understood that the activation of the reversing valve occurs based on the remaining marginal conditions of the transmission, at least for the aforementioned critical cases. For this, the control device for the control valve can be used to activate the reversing valve, wherein the determinants for the transmission operation are supplied to this control. However, this also requires a special activation member that is triggered by the control. Another option therefore may be to activate the reversing valve with the aid of the pressure existing in the pressure medium intake line. Since this pressure exerted by the pressure medium is derived from the valve position specified by the control, a corresponding determinant is automatically provided for adjusting the reversing valve. However, the determinant for this design option is also obtained automatically if, during a pause in the transmission operation, the transmission ratio is to be changed, so as to require the emptying of the pressure cylinder. However, this can only be helpful for a rapid change in the transmission ratio.